1. Field of the Invention
This invention relates broadly to card panels which are coupled to a backplane, e.g., in a telecommunications network. More particularly, this invention relates to electromagnetic interference reduction elements for the card panels.
2. State of the Art
Card panels, each of which provides particular functionality, are `plugged` into backplanes or racks. Such card panels are commonly used in telecommunications networks. However, when a plurality of circuit cards and/or panels are provided in a rack, the circuit cards produce electromagnetic radiation in the form of electric and magnetic waves that may adversely interfere with other cards inside the rack and electronic equipment outside of the rack. The spaces or gaps between adjacent card panels provide a path through which electromagnetic radiation may escape, unless the spaces or gaps are provided with a conductive barrier to prevent the electromagnetic interference (EMI).
Referring to prior art FIGS. 1 through 3, a card panel 10 includes a generally C-shaped, conductive bracket 12 and a circuit board 14 coupled to the bracket. The bracket 12 includes a front side 16 and first and second lateral sides 18, 20. The board 14 includes circuitry, e.g., integrated circuit packages 22, other circuitry 24, ports 26, connectors 28 for coupling the board 14 to a backplane, and indicator LEDs 30. The board 14 is coupled to the inner surface 32 of the first side 18 of the bracket 12, while the outer surface 34 of the first side is substantially planar. The front side 16 is typically provided with cut-outs which receive therethrough the ports 26 on the board 14 to permit user-assigned connectivity to other components, and may also permit the LED indicators 30 on the board 14 to be seen therethrough. A cosmetic face plate 36 is provided over the front side 16, and includes printed indicia 38 thereon to provide identifying information to a user. The outer surface 40 of the second side 20 of the bracket 12 is provided with an elongate copper spring 42 which performs as a conductive barrier. As shown in FIG. 2, the spring 42 has a generally triangular cross-section with two lower flanges 43, 44, and raised portion 45 provided with a plurality of gaps 46 which form a plurality of independently compressible spring portions 48.
When the card panel is placed in a rack, the spring 42 contacts the first side 18 of another card panel already positioned in the rack. The independently compressible spring portions 48 of the spring 42 act to form an electrical bond between the panel to which the spring is attached and the first side of another card panel or conductor of the rack. In this manner, the spring 42 functions to conductively contact a conductive portion of an adjacent card or a conductor on the rack and thereby ground the card panel 10 to reduce EMI.
In the prior art, several different assemblies are provided for coupling the EMI reduction spring 42 to the card panel 10. According to one assembly, as shown in FIG. 2, the spring 42 includes an inwardly bent flange 44 which is coupled to the outer surface 40 of the second side 20 with an adhesive 50. The adhesive 50 must be positioned on the outer surface 40 adjacent a free end 52 of the second side 20 (away from front side), such that when the card panel 10 is inserted into a rack, the spring is not inadvertently caught and removed. Turning now to FIG. 4, in another prior art spring assembly, the spring 42a includes an inwardly bent flange 43a, and an outwardly bent flange 44a. The outwardly bent flange 44a is coupled by an adhesive 50a to the outer surface 40a of the second side 20a of a bracket 12a of a card panel.
However, both of these prior art assemblies have several disadvantages. First, the springs 42, 42a may tear off, especially upon removal of the card panel from the rack. Second, it is easy to assemble the spring incorrectly, i.e., with the adhesive away from the free end 52. Such assembly may cause the spring 42, 42a to be undesirably deformed, i.e., with the flange 43, 43a being bent away from the second side 20, 20a upon insertion of the card panel into a rack. Such undesirable deformation makes the spring unusable and compromises the integrity of the EMI-reduction barrier. Third, the adhesive may dry up or delaminate under certain conditions, such as relatively hot or cold temperatures, over a period of time.
Referring now to FIG. 5, in yet another prior art spring assembly which does not necessitate the use of an adhesive, a track 54b is coupled to the outer surface 40b of the second side 20b of a bracket 12b. The track 54b is secured to the second side 20b with a plurality of screws or rivets 56b. The spring 42b is then slidably disposed over the track. This assembly also has several problems. First, a large number of rivets 56b are required to hold the track 54b against the second side 20b. Therefore, a time consuming process for assembly of the track to the bracket is required. In addition, the rivets 56b may interfere with ports and circuitry on a circuit board coupled to the bracket 12b. Second, the assembly, requiring a discrete track member 54b and a large number of rivets 56b for coupling the track member to the bracket, is relatively expensive to manufacture. Third, the track does not always lie flat and straight, and may bend, twist, or bow relative to the bracket 12b. Such irregularities may cause the spring to be inadvertently removed by an adjacent card panel and will create discontinuities in the EMI barrier.